This invention relates in general to antennas, and more specifically to microstrip dipole antennas formed on high permitivity dielectric substrates.
Conventional printed-circuit dipole antennas are constructed on low permitivity dielectric substrates. These low permitivity dielectric substrates are relatively thick. Furthermore, the dipoles are relatively large and require large resonant cavities. These large antennas cannot be used directly with monolithic microwave integrated circuits (MMIC), but require additional interconnecting circuitry for MMIC applications.
To decrease the size of the antenna and make it compatible with MMIC technology, the antenna substrate must be reduced in thickness. Additionally, the permitivity of the substrate must be increased. One dipole antenna having a higher permitivity substrate has been designed using a Bawer and Wolfe Balun. This balun couples the two dipole arms to a microstrip transmission line by means of parallel conductors. The conductors form a rectangle having 90 degree corners. The Bawer and Wolfe Balun, however, generates significant amounts of spurious radiation from its resonant transmission line conductors, particularly when formed on relatively high permitivity substrates. The spurious radiation reduces the desired dipole antenna efficiency.